Biomaterials have been used for implantation into the human body to act as supports for wound and solid tissue healing. Matrices useful for this purpose should have the ability to adhere and conform to the wound site and surrounding tissue. Ideally, they also should facilitate accumulation of fibroblasts, endothelial cells and wound healing regulatory cells to promote connective tissue deposition and angiogenesis.
U.S. Pat. No. 4,849,285 to Dillon is directed to a composite, self-supporting agglomerated microstructure useful as a surgical implant. The macrostructure is a matrix of polytetrafluoroethylene resin and cured silicone that has uniformly distributed within it a particulate material. These particulates have a maximum size of about 2000 microns and may be hydroxyapatite or tricalcium phosphate. This particular macrostructure, therefore, is a composite of ceramic particulate material and organic biomaterials that is uniformly permeated by a network of open pores. The pores are formed by incorporating sodium chloride into the composite and thereafter leaching it out in the manufacturing process.
U.S. Pat. No. 4,843,112 to Gerhart et al. is to a bone cement composed of a particulate biocompatible calcium phosphate ceramic and a resorbable calcium salt disperses in a crosslinked biodegradable polyester matrix. Pores are created in the matrix by body fluids creating small voids or cavities in the polymer matrix.
U.S. Pat. No. 5,141,522 to Landi et al. describes a composite of two or more biocompatible polymers useful for mammalian tissue repair. One of the polymers is polytetrafluoroethylene (PTFE), which is the reinforcing binder. A bioabsorbable component that may be a lactone, carbonate or a lactide, is contained within the structure of the PTFE and serves to enhance ingrowth of tissue.
Additional disclosures of PTFE compositions useful as implants include, but are not limited to U.S. Pat. Nos. 5,141,522; 5,098,779; and 4,863,974. The PTFE component of these compositions serves as a nonabsorbable microfibrillar structural support. A bioabsorbable component is contained or coated on the structural support. The PTFE is polymerized prior to implantation of the compositions.
U.S. Pat. No. 4,373,217 to Draenert is directed to a polymeric implant material that has an acrylate, polymethacrylate or copolymer base with dispersed resorbable tricalcium phosphate of 50 to 300 microns with an available pore volume of less than 0.1 mL/g. This particular material is said to allow for a firm bond between implant and body tissue. Resorption of tricalcium phosphate particles at the surface of the implant are resorbed into the body is said to promote bone growth in the marginal porosity produced. In order to ensure absorption of liquid monomer into the porous calcium phosphate, a filler that is also resorbable in the body is included to fill the pore volumes of the calcium phosphate.
U.S. Pat. No. 4,898,734 to Mathiowitz et al. also involves a precast solid polymeric implant material. A continuous polymeric matrix made of, for example, polyurethane or polystyrene, is embedded with microcapsules or microspheres that may contain material for subsequent release. The spheres may be removed from the matrix by bioerosion. For creation of a vascular graft, erodible microspheres are entrapped within a tube-shaped slower-degrading polymer matrix. Rapid erosion of the spheres results in pores for cell seeding and vascularization with the matrix providing support until there is sufficient cell growth to create structural integrity.
U.S. Pat. No. 4,950,483 to Ksander et al. describes a collagen implant useful for wound healing. The implant is made of collagen and has a bulk density of 0.01 to 0.03 g/cm.sup.3 and is said to have a pore size sufficient to permit cell ingrowth. Bioactive agents such as FGF and TGF-.beta. may be incorporated into the implant.
U.S. Pat. No. 5,077,049 to Dunn et al. is directed to a method for restoring periodontal tissue. A biodegradable liquid polymeric systems designed to generate a porous structure when cured into a barrier membrane, is administered to the soft-tissue defect. The pores will form as a result of water-soluble material included in the liquid material. The liquid material injected into the defect provides a scaffold that is filled with new bone cells that gradually replace the water-soluble polymer.
U.S. Pat. No. 4,902,295 to Walthall et al. involves a transplantable artificial tissue. The tissue is made by mixing a polymerizing matrix with reversible gel precursors in an aqueous solution with viable cells. The gel, which may be alginate, a gum or agarose, is then dissolved to provide a porous matrix for implantation.
None of the above-described references describes a biomedical implant material with a differentially degradable matrix and porosifying agent where polymerization occurs in situ or where the matrix is precast and is made of a biopolymeric material.